The field of light emitting modules includes a large variety of different light emitting modules regarding use light sources, construction, optical characteristics, etc. Important characteristics for many applications of light emitting modules are that they shall be arranged to provide uniform illumination. Another important aspect of light emitting modules is the increasing need of providing energy efficient light emitting modules. One example of light emitting modules being energy efficient is light emitting modules being based on LEDs. However, LEDs are point sources and hence there is a problem of producing LED based light emitting modules providing uniform illumination.
In order to obtain uniform light various strategies have been adopted. One of the strategies is based on the use of solid wave guides with out-coupling structures. However, such wave guides can absorb light and coupling light into a solid wave guide can give losses. Another strategy is placing large number of LEDs at the bottom of a mixing chamber in combination with a diffuser for obtaining uniform illumination. However, placing LEDs at the bottom surface can decrease the reflectivity and thus reduced system efficiency. Furthermore placing large number of LEDs at the bottom of a mixing chamber is costly and it can also lead to excess heating due to the concentration of LEDs to a small area.
Hence, there is a need for alternative light emitting modules being able to provide uniform illumination.